Television



Feb. 22, 1938.

F. SCHROTER TELEVISION Filed Jan. 5, 9

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ENVENT QR FRITZ $6580??? I ll Patented Feb. 22, 1938 UNITED STATES PATENT OFFICE TELEVISION Germany Application January 5, 1935, Serial No. 509

In Germany December 12, 1933 2 Claims.

This application relates to a system and method of photoelectric scanning for television work.

A method has been disclosed in the art which is adapted to store the effect of the picture line corresponding to the elementary picture. For this purpose, the picture, for instance, by means of a mirror or reflector wheel insuring change of picture and being of large aperture is moved over a number of extremely small photoelectric cells which, as known in the art, represent the electrodes or plates of as many individual condensers working with a common or joint cooperate plate or electrode. As many condensers are aligned as there are grate elements in the picture line. For

' the duration of a line, therefore, the photoelectric effect is accumulated. In connection therewith the various condenser elements are scanned by means of a cathode ray pencil sweeping thereover at line-speed so that, by the action thereof, each element furnishes a current impulse corresponding to its charge and which controls the grid of an amplifier tube.

The object of the present disclosure is an improvement upon the above described arrangement previously disclosed. The present improvement makes it feasible to enlarge the photoelectric surfaces corresponding to the picture elements or the condensers associated therewith to a size greater than what would be admissible with the present day means in the case of scanning by the aid of a cathode ray pencil moved along a straight line. It has been ascertained that in photoelectric picture scanning the gain in useful light current will be so much larger, the larger the size in which the picture field to be transmitted may be imaged on the scanner. According to the present invention the plane of the image of the object to be transferred on the photoelectric cell will present line lengths ranging between and 1 m., in other words, lengths that would be hard to attain in a cathode ray oscillograph with normal line motion, not to mention the impossibility of making the scanning free from distortions.

Another very essential merit of the improved embodiment of the basic idea of the invention disclosed in the prior art invention above referred to resides in this fact that the various photoelectrio surfaces are not themselves struck by the high speed electrons of the cathode ray pencil and that they are thus safeguarded from destructive effects inevitably arising in the arrangements suggested in the earlier art. In these the scanning electron ray pencil strikes the photoelectric cell areas directly With full energy; the

result is that the sensitiveness of the same to incident light may be unfavorably affected and turn out to vary from one local spot to another.

A third advantage of the arrangement hereinafter to be described is that even with large areas of the photoelectric surfaces of the photocell row, it is feasible to render the sensitivity of the constituent elements practically stable, namely, by averaging. Another point is that the requisite accumulating condensers can be made of microscopic size so that the production by chemical treatment of the microscopic constituent condensers distributed over a scanning surface which is quite delicate and unreliable can be dispensed with. Other advantageous features of the scheme here disclosed may be regarded to reside in that the electron switch" may more readily be made of the proper dimensions, while its decisive quantities such as scanning speed, uniformity of the same along the line, or lack of uniformity (for compensating distortions in receiver) may be governed more easily than is true of the embodiment disclosed in the parent patent application predicated upon and patterned after the cathode ray oscillograph. What is thus attainable is an extremely high precision of scanning with an incidentally great geometric freedom from distortion of the picture resolution.

Now, the fundamental idea of the present addition patent application consists in this feature that the row of photoelectric cells irradiated by an active picture line is accommodated ins de a tubular vacuum container, while the cathode ray scanner separately therefrom is accommodated inside another vacuum vessel. The constituent photoelectric cell elements through separate leads are united with a corresponding number of electrodes over which the scanning cathode ray pencil is swept, in synchronism with the line resolution, in the television receiver. In addition to the advantages hereinbefore mentioned, such separation of the row or bank of photocells from the scanning electrodes insures the further merit that the cathode ray pencil is capable of a complete rotation. Incidentally, there is brought about a transformation of the dimensions which is of advantage in the present practical use. Fundamentally speaking, it is, of course, also feasible to cause the cathode ray pencil, instead of a circular movement. to go through a rectilinear line motion (obtainable by a Kipp or relaxation wave scheme) along a linear disposition of scanning electrodes, although it will be evident that in such an arrangement, because of the intervening spaces necessary between the electrodes, the limits as regards reduction of overall length are more restricted than in the case of a circular scheme. Optimum dimensions will be found if the cathode ray pencil is caused to describe a spiral motion of constant traveling speed by ways and means known in the prior art, and if the scanner electrodes are disposed in such a spiral.

One exemplified embodiment is shown in the drawing. The picture to be transmitted by the aid of an objective I by way of a rotating reflector prism 2 is projected into the plane of the row of photoelectric cells 3 which are accommodated inside a distinct light permeable vacuum vessel along a straight line and are thoroughly insulated from one another in spite of minimum intervening distances between the elemcnts. In other words, the brightness distribution of a whole picture line is brought to act upon the row of cells so that the photoelectric action is accumulated throughout the duration of a picture line. The joint co-operative coat 4 of all activated surfaces or accumulating condensers is connected by way of a resistance 5 with ground and at the same time through the blocking condenser 6 with the grid of the amplifier tube i. From the various photoelectric elements insulated wires 8 relatively balanced in regard to resistance and capacity are brought to a corresponding number of scanning electrodes 9 which are circularly disposed inside the cathode ray tube I0. Only a few of the connections and scanning electrodes are indicated for the sake of clearness of illustration. The circular movement of the cathode ray pencil which is indicated by the broken line i3 occasions here a rofury magnetic field which is produced by the coil pairs ii and I2. The source of the electron pencil is connected by lead I4 with the ground. In lieu of the rotary magnetic field, recourse could, of course, be had also to a rotating electrical field.

The frequency of the rotating field is transmitted to the receiving end by way of the picture transmitter or of a distinct path where it serves to synchronize the line frequency of the picture re-ereating spot. In order that for distortion correcting purposes (e. g., if in the receiver the means for the complete regularization or stabilization of regularity of line motion are to be saved) a corresponding non-uniform velocity of the scanning cathode ray pencil may be secured, the distances intervening between the various electrodes 9 may be suitably varied. Inside certain limits such an effect is also obtainable by that the circular movement of the pencil is de- Fm med to result in an ellipse.

The function (mechanism) of photoelectric scanning is as follows: According to the local intensity of illumination the constituent condensers formed by the elementary photoelectric cells and cooperative coat 4 (optionally with additional capacity inside or outside the tube) at the end of a line period will have been charged up to a definite voltage level (provided that the attaining of the saturation potential as defined by the fundamental photoelectric equation is avoided). By the positive charge of the photoelectric a corresponding quantity of negative electricity is held on electrode 4. However, at the instant when the cathode ray pencil l3 by way of the coordinated scanning electrode supplies to a given element of row 3 negative charge so that the positive charge thereof becomes compensated. there is set up an impulse of current in the resistance 5 and as a consequence, through condenser 6, a corresponding control impulse at the grid of the tube I. This impulse which is a function of the picture brightness through the following amplifier acts upon the television receiver as known in the art.

Having thus described the invention, what is claimed is:

1.. In combination, optical means for scanning an object by elemental linear strips, an evacuated envelope having means included therein for developing an electron beam, said envelope having positioned therein in register a plurality of discrete conducting elements, a plurality of light sensitive elements without said envelope and insulated each from the other, means for electrically joining each of the said discrete conducting elements to at least one of said light sensitive elements, means for sequentially projecting the elemental linear light strips upon the aforesaid light sensitive elements, means for developing individual electric charges on each of the discrete conducting elements proportional to the light intensity impinging on the light sensitive element to which it is electrically joined, means for storing said individually developed charges, means for circularly directing the electron beam sequentially across the conducting elements for discharging said stored charges, and a load circuit connected to said discharging means.

2. In combination, optical means for scanning an object by elemental linear strips, an evacuated envelope having means included therein for developing an electron beam, said envelope having positioned therein in register a plurality of discrete conducting elements, a plurality of light sensitive elements without said envelope and insulated each from the other, means for electrically joining each of the said discrete conducting elements to at least one of said light sensitive elements, means for sequentially projecting the elemental linear light strips upon the aforesaid light sensitive elements, means for developing individual electric charges on each of the discrete conducting elements proportional to the light intensity impinging on the light sensitive element to which it is electrically joined, means for storing said individually developed charges, electronic means for sequentially discharging said stored charges, and a load circuit connected to said discharging means.

FRITZ scHRoTER. 

